1. Field of the Invention
The present invention generally relates to a magnetic tape cassette and more particularly to a structure for fixedly supporting a tape guide in the magnetic tape cassette.
2. Description of the Prior Art
In a cassette tape assembly such as a video tape cassette, there is usually provided tape guide means for guiding properly the transportation of a magnetic tape. FIG. 1 of the accompanying drawing is an exploded perspective view of a casing of a video tape cassette showing in detail only the tape guide mechanism for the facilitation of understanding.
Referring to the figure, reference numeral 1 denotes an upper casing half and 2 denotes a lower casing half. Mounted in the lower casing half 2 of the cassette along a path of tape transportation are a metallic guide pin 3, a fixed metallic cylindrical tape guide 5 supported by a supporting pin 4 of a plastic material, a fixed metallic cylindrical tape guide 7 supported by a plastic supporting pin 6 and a plastic guide roller 9 supported on a plastic pin 8 which are disposed in this order as viewed from the magnetic tape feeding side. Among these guide members, the tape guides 5 and 7 play the most important role. Since these tape guides must be of a low friction and have a high abrasion withstanding capability in order to ensure a proper transportation of the magnetic tape, they are usually formed of a metal such stainless steel, a hard-plated brass or the like and finished with high precision.
Typical mounting methods of the cylindrical tape guides 5 and 7 adopted heretofore are illustrated in FIGS. 2, 3, 4 and 5 of the accompanying drawings. In this conjunction, reference may be made, for example, to Japanese Utility Model Publication No. 35985/1981, the gist of which is depicted in FIGS. 2, 3, 4 and 5 and is briefly discussed below. Referring to the figures, the upstanding supporting pin 4 is anchored in a supporting platform 10 formed in the lower casing half 2 and the cylindrical tape guide 5 is fitted around the supporting pin 4. In the state where the upper half 1 is assembled on the lower half 2, the tape guide 5 is sandwiched under pressure between the supporting platform 10 of the lower half 2 and that of the upper half, whereby the tape guide 5 is fixedly secured.
A semi-cylindrical tape guide has also been proposed from the view point of reducing the cost of material and for other reasons. Typical examples of such semi-cylindrical tape guide are disclosed, for example, in Japanese Utility Model Publications Nos. 3420/1984 and 5660/1986. According to these publications, the mounting of the semi-cylindrical tape guide has heretofore been realized by using a bonding agent or a bilateral adhesive tape.
With the tape guide mounting techniques known heretofore, however, the position of the tape guide can not always be established with satisfactory accuracy. The reason may be explained by the fact that difficulty is encountered in realizing precisely the diameter and the true circularity of a part for forming the pin 4 in a die for molding the lower half (as well as the upper half) in case the tape guide is cylindrical. In order to solve this problem, a precise finishing is required, which however involves a very time-consuming processing, leading to a significant increase in the manufacturing cost. In general, it is very difficult to assure the true circularity and precision size for the pin 4, giving rise to a problem that the tape guide can not be fitted on the supporting pin 4 because of tightness or tape guide rotates or jolts around the pin 4 due to looseness.
On the other hand, in the case of the semi-cylindrical tape guide, variation in the amount of the bonding agent and the thickness of the bilateral adhesive tape presents a cause for positional deviation or variation of the guide, making it difficult to control precisely the position of the tape guide. Besides, after the mounting of the semi-cylindrical tape guide, degradation in the strength of adhesion in the course of time lapse presents another problem to be solved.
A further problem can be seen in that the tape guides are secured to the tape cassette by using the supporting means designed specifically for the guides, respectively. Consequently, the structures of the upper and lower halves of the cassette casing necessarily differ in dependence on the types of tape guides, to serious disadvantage for the manufacture.